Im really bad at chemistry help!

a) sodium and chlorien atoms bond to form salt molecules

Explanation:

Pretty much all the other reactions can be reversed. Ice melting to form water can go back to being ice under freezing temperatures. H2O is H2O. It doesn't become a new compound due to temperature changes unless it is introduced to other elements. Carbon dioxide freezing to forming dry ice is typically a physical rxn. Salt and water mixing to form salt water although is chemical, can be easily reveresed if you were to boil off the water: all that would remain is salt.

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